With the miniaturization of electronic equipment, the number of electronic parts to be accommodated in a unit volume has increased. An element such as a transistor, a diode, or the like relating to an interfacial physical phenomenon can be made extremely small with an improvement of an integrated circuit technique. Since a capacitor has a characteristic that its electrostatic capacity is proportional to an electrode area, it is not easy to realize a capacitor having a large electrostatic capacity and a small size at the same time. Capacitors designed to be large in electrostatic capacity and small in size, such as a laminated ceramic capacitor, an electrolytic capacitor, an electric double-layer capacitor, a thin film capacitor and the like, have been put into practical use.
A laminated ceramic capacitor is produced in the following manner: Powder of a raw material having a high dielectric constant, such as perovskite-type composite oxide, e.g., BaTiO.sub.3, is made into a slurry by using an organic binder, and then formed into sheets. Internal electrodes are formed on the respective sheets, and then the sheets are laminated and sintered. That is, a large electrostatic capacity is realized by the use of a high dielectric constant material and by the increase of the electrode area due to lamination. However, it is generally necessary to sinter the powder of the raw material having high dielectric constant at a high temperature not lower than about 1200-1900 degrees Celsius. It is therefore necessary to use an expensive noble metal such as silver, palladium or the like, as the internal electrodes, and a large amount of energy is required for production, and thus not only the production cost is high but also the production process is complicated. Further, since the thickness of the dielectric is about 10 .mu.m, there is a limitation on further reduction in thickness.
In both the electrolytic capacitor and the electric double-layer capacitor, it has been attempted to increase the surface area of the electrodes to the utmost by making the surface of electrodes uneven. These capacitors however have the following disadvantages.
The electrolytic capacitor, such as an aluminum electrolytic capacitor or a tantalum electrolytic capacitor, is designed so that an anodized film of aluminum or tantalum as an electrode metal is used as a dielectric material. There is therefore no room for selection of the dielectric material so that such an electrolytic capacitor cannot be provided with various capacitor characteristics. Further, the specific dielectric constant of the oxide of those materials is about 90 at the most and is remarkably lower than 2000 or more, which is the value of a high dielectric constant material such as BaTiO.sub.3, or the like, used in a ceramic capacitor. Accordingly, even if the electrode area is made large, the capacity of the electrolytic capacitor is relatively low. Moreover, the resulting electrolytic capacitor has a polarity.
The electric double-layer capacitor is not only poor in shock resistance because it contains electrolyte but also low in working voltage, although it is possible to improve the ratio of its electrostatic capacity to its volume.
The thin film capacitor is designed so as to reduce the thickness of the electrode and the dielectric material to the utmost, and generally its film thickness is made to be several hundred nm or less. Reduction in thickness of the dielectric material causes the volume occupied by the dielectric material to be decreased and also the electrostatic capacity to be increased under the condition of the same electrode area. In the thin film capacitors, an oxide thin film, such as Ta.sub.2 O.sub.3 or the like produced by a vapor phase method, such as evaporation, sputtering or the like methods, is used as the dielectric material. However, its dielectric constant is 90 at the most and is not sufficient for realizing a large capacity.
It has been proposed to reduce a high dielectric constant material such as BaTiO.sub.3 in thickness by using a vapor phase method similarly. In this case, it is possible to obtain a specific dielectric constant of several hundred, which is higher than that of an oxide thin film of Ta.sub.2 O.sub.3, while still being lower than the value of several thousand in the case of a film thickness used in a ceramic capacitor, because a high dielectric characteristic does not sufficiently appear when the film thickness is reduced. Further, since the technique of manufacturing thin film capacitors does not include a lamination technique which is an advantageous feature in the production of the ceramic capacitors, nor a technique for forming a large surface area film which is an advantageous feature in production of the electrolytic capacitors and electric double-layer capacitors, it is impossible to expect an increase in electrode area, so a capacitor of a large capacity has been not yet been realized by use of only a thin-film technique.
As is apparent from the foregoing explanation, in order to realize, at a low cost, a capacitor which is small in size, light in weight and large in electrostatic capacity, it is necessary to solve three problems: it is desired to use a dielectric material having a high dielectric constant which cannot be realized by an electrolytic capacitor; it is desired to make the dielectric material into thin films to an extent corresponding to a thin film capacitor; and the electrode area is to be increased by lamination by using the thin films of the dielectric material in the same manner as a laminated ceramic capacitor.